The collection of portable batteries at end-of-life is the first step in waste management and circular economy towards material recycling and recovery of raw materials. The collection facilities are placed as close as possible to the end user. The safety of intermediate storage facilities must be ensured.
The increasing amount of lithium-based batteries in many waste streams poses a fire safety challenge for waste management. Just a small number of hazard assessments, as for other material streams available, are found for portable battery collection. The growing proportion of lithium in the amounts placed on the market is already apparent in the composition of the collected masses. Due to their composition, lithium batteries and lithium-ion accumulators cause a significantly higher hazard than other battery types.
Factors influencing the occurring fire risk and the possible consequences are investigated. The expected causes for ‘thermal runaways’ differ from those for the operational phase. The waste nature of the batteries leads to different characteristics. Some impact factors have not been studied qualitatively or quantitatively in the evaluated literature. The effects of battery collection fires are comparable to typical fires in the same scale.
Studies on the probability of short-circuits in battery piles are not yet available. This thesis presents a new approach using rigid body dynamics in the free software 'blender' for investigation of the geometrical arrangement of batteries in random fills. The formed short circuits are detected and characterised further. A simplified electrical model is used to estimate the heat generation of each battery and to describe the likelihood of subsequent ignition within the bulk. The influence of different parameters is investigated in several test series and a sensitivity analysis is presented.
The simulation results indicate that the main impact factor on the formation of short circuits is the proportion of button cell batteries. If the fraction is 5 %, the evaluation results in a short circuit rate of about 0.4 % of the cells. In a pure coin battery fraction, this proportion is approx. 83 %. Based on the number of batteries in interconnected networks and the calculated electrical currents, it can be shown that the formation of short circuits across many cells in serial connection can be considered as highly unlikely. With the correlations found, an estimate about the distribution of heat release within the bulk can be made.